The present invention relates generally to wireless communications, and more particularly to a hub and probe system and method for internal communications within structures, particularly at frequencies in the range of 0.5 to 100 MHz.
Communications within buildings and other enclosed spaces have long presented problems. Communication wiring, such as for local area networks, is effective but suffers from problems with installation costs, limitations on connection locations and the need for periodic upgrading when technology advances. Metallic structural members, interior furniture, plumbing and electrical wiring all have a tendency to interfere with conventional wireless communications. Outside interference, such as from galactic noise and human generated electromagnetic sources also frequently interferes with the quality and efficiency on in-building communications.
As described in the inventors prior application, a neglected frequency band in the electromagnetic spectrum, at least from the standpoint of communication utilization, is that in the 0.5-100 MHz range. Much of this range is traditionally considered to be less than useful, and is accordingly less regulated by government entities. An example of this in the United States is that Part 15 of the FCC Rules apply in this range. One reason that this range is not widely utilized is that the waveforms have sufficiently long wavelengths that structural interference affects transmission and reception. However, with the inventor""s technology it has become possible to harness this range of frequencies and to turn the factors which have been hindrances into advantages.
An area of electromagnetic phenomena which has been little understood and utilized traditionally is that dealing with evanescent (non-propagating) waves. Commercial utilization of these phenomena have been rare. The phenomena are known and observed in waveguide technology, but are ordinarily a hindrance, and limit the utility of structure near what is known as xe2x80x9ccut-offxe2x80x9d.
Cut-off occurs for conventional propagation in hollow pipe waveguides when the size of the hollow pipe waveguide is less than one-half (xc2xd) of the wavelength at the operating frequency. When these conditions obtain, the transmission losses are very high but not infinite. The expression for attenuation below cut-off in ideal waveguides, Equation 1, may be written:
xcex3=2xcfx80/xcexc{square root over (1xe2x88x92(f/fc)2)}xe2x80x83xe2x80x83(1)
where:
xcex3=attenuation
xcexc=cut-off wavelength
f=operating frequency
fc=operating frequency at cut-off
where the wavelength, f is approximately equal to 11.8/f (GHz) in inches.
As f is decreased below fc, xcex3 increases from a value of 0 approaching the constant value of 2xcfx80/xcexc, when (f/fc)2 less than  less than 1.
The amount of attenuation is determined only by the cut-off wavelength of the waveguide, which is in general proportional to the transverse size of the waveguide, so that the value of xcex3 may be made almost as large as one pleases by selecting a low cut-off wavelength or a high cut-off frequency (small pipe size). Since (1) holds for any wave in any shape of guide, it follows that choices of wave type and guide shape cannot influence the attenuation constant except in so far as they fix the cut-off wavelength xcexc.1 
Wave motion, forming the core of many subjects in physics, is a prominent (interdisciplinary) topic in many textbooks.2 While traditional wave motion is often dealt with in great detail (for good reasons), the theory of evanescent waves is often only mentioned in passing.
Such small mention is by no means justified: evanescent wavesxe2x80x94originally indeed introduced as convenient mathematical tools having no application in mind3 4xe2x80x94matured in the last decades to a topic of its own intrinsic interest finding a steadily increasing number of applications in basic as well as applied research and in industry.
1 xe2x80x9cFields and Waves in Modem Radioxe2x80x9d, Simon Ramo and John Whinnery, pg 386-387, dated May 1956 
2 ON EVANESCENT WAVES, A. Stahlhofen and H. Druxes, Univ. Koblenz, Inst. f. Physik, Rheinau 1, D-56075 Koblenz, Germany 
3 Bryndahl, O., xe2x80x9cEvanescent waves in optical imagingxe2x80x9d, in Progress in Optics (American Elsevier Publishing Co, New York 1973), pp 169-221 
4 Hupert, J. J., Appl. Phys. 6, 131-149 (1975) 
Any propagating wave is converted into an evanescent wave when hitting a classically forbidden region (below cut-off). In this case, at least one component of the wave vector becomes imaginary or a complex value and the wave experiences exponential damping when operating in this region (the cut-off effect described above). Such waves are used as diagnostic tools in many contexts involving waveguides; applications range from diverse areas of solid state physics and microwave-technologies. Explicit examples show that evanescent waves play an important role in microwaves, optics, and quantum mechanics. Despite the fact that all of these systems are governed by different wave-equations, different dispersion laws, different energy regimes and completely different structures and sizes, wave motion in the respective systems under consideration often involves evanescent waves.
The typical mechanisms accounting for the existence of evanescent waves are: 1) conversion into other forms of energy in lossy media, 2) cut-off modes in certain directions resulting from reflections in lossless media, 3) gradual leakage of energy from certain guiding structures and 4) mode conversion produced by obstacles or by changes in guiding structures.
Evanescent waves have some peculiar properties sometimes defying intuition. As a typical example the fact was mentioned that they operate in the forbidden region (below cut-off) experiencing exponential damping. Wave motion involving evanescent waves is easily demonstrated with electromagnetic waves using microwaves. A guide to many experiments involving evanescent waves is provided by PIRA, the xe2x80x9cPhysics Instruction Resource Associationxe2x80x9d located at http://www.physics.umd.edu/deptinfo/facilities/lecdem. This source provides short descriptions of hands-on as well as more sophisticated experiments with evanescent waves referring for details to easily accessible literature.
It is now established that electromagnetic connectivity can be achieved by the use of evanescent non-propagating waves below cut-off or propagating waves above frequency cut-off. Some methodology must be developed which can inject currents into the metallic elements of a structure in order that evanescent waves be generated in the cut-off region. For frequencies above the cut-off region more traditional antenna technologies can be used.
Although the phenomena relating to evanescent waves and other wave characteristics resulting at wavelengths below or near cut-off regions are known, they have not heretofore been meaningfully commercially utilized. In general, these phenomena are considered to be hindrances and nuisances, rather than opportunities for actually enhancing communications. In this light, there remain many opportunities for utilization and improvement, to be addressed by the present invention and the Inventor""s related inventions.
Accordingly, it is an object of the present invention to utilize the characteristics of electromagnetic energy in frequencies which produce evanescent waves, and in near cutoff frequencies, to provide a medium for effective communication within structures.
It is another object of the present invention to provide a medium for an exciter to send and receive information wirelessly within a structure.
It is a further object of the present invention to provide a probe on remote devices for receiving information through the medium and sending information thereto.
It is yet another object of the present invention to provide for a remote device probe that creates a radio frequency to transmit data to the exciter and ultimately to the medium for communicating with devices outside the structure, as well as with other remote devices in the structure.
Another object of the present invention is to provide a probe that creates an electromagnetic environment for coupling the transmission of signals to the conducting elements of the building and thereby the exciter.
Briefly, a preferred embodiment of the present invention is an exciter system for energizing and operating with the Electromagnetic Field Communications System for Wireless Networks. This is a wireless technology scheme which allows wireless communication within a structure. In a typical residential, commercial or industrial building, the exciter performs the function of exciting the a conductive framework, formed of metallic elements existing within the walls of the structure, whether they be electrical wires, metal walls, plumbing or any combination thereof This wireless system is initiated by a hub and controller network which is connected to and drives the exciter. The exciter in turn energizes the conductive framework in the building walls for use by any number of remote wireless receivers situated within the structure. The basis for this technology is disclosed and contained in the inventor""s U.S. Patent Application entitled Electromagnetic Field Communications System for Wireless Networks, Ser. No. 09/340,218, filed Jun. 25, 1999. The hub and controller network along with the exciter works to allow a complete wireless system to operate within a structure that would otherwise not be possible.
The Hub receives information from devices outside of a wireless communication structure. These external devices may be hard wired to the Hub or they may connect wirelessly. The Hub may also receive information from remote devices in the structure. The Hub transmits this data to the exciter by sending a frequency signal thereto. The exciter creates evanescent waves and relays the radio frequency to a probe on a remote device within the wireless communication structure via the evanescent waves. The probe passes the information to applications electronics, such as telephones, PCs, etc. Outgoing communications from the remote device are sent to the exciter via the probe when the probe electromagnetically couples radio frequency signals to the conductive elements in the walls of the structure. The exciter receives the radio frequency signal and passes the signal to the Hub, where it may be communicated externally or internally to other remote devices.
An advantage of the present invention is that it provides a way to activate an effective communications bubble within a building or structure which minimizes interference from outside sources, such as galactic noise and man made radio frequency signals.
Another advantage of the present invention is that the Hub controls the dissemination of incoming and outgoing communications as related to external devices.
Yet another advantage of the present invention is that it minimizes noise interference from sources within the building.
A further advantage of the present system is that it can operate under Part 15 of the FCC rules.
Yet another advantage of the invention is that it uses the size of a structure to eliminate the need for very large antennas.
Another advantage of the present invention is that the remote device probe is compact and is not direction sensitive.
It is another advantage of the present invention that a broad frequency range is created by the exciter, hub, and probe as a system.
A further advantage of the present invention is the flexibility within the broad frequency range, created by the linear and bilateral nature of the system, to utilize all means of modulation techniques including Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.